Harmonic amplitude selector for signaling systems

ABSTRACT

676,276. Telephone transmission systems. STANDARD TELEPHONES &amp; CABLES Ltd. Sept. 15, 1950 [Jan. 21, 1950], No. 22726/50. Class 40 (iv). [Also in Group XXXVI] In an arrangement for determining the amplitude of the harmonics of a variable fundamental # 0  in a complex signal, a signal representing the fundamental frequency controls a series of constant-amplitude sources of oscillations to cause them to produce frequencies F 1 +# 0 , F 2 +2# 0 , ... F n +nf n , where F 1  ... Fn are fixed frequencies. These frequencies are then mixed with the complex signal to produce frequencies F 1  ... F n  having amplitudes proportional to those of the respective harmonics. The arrangement is suitable for use in a system such as that described in Specification 667,196 in which a voice signal is represented in transmission by signals representing the amplitude and frequency of the fundamental, and the amplitudes of the harmonics. As shown, Fig. 1, the fundamental frequency selector 2 feeds a circuit 3 whose output consists of a D.C. voltage proportional to the frequency of the fundamental. This voltage is fed to thermionic reactances 7, 8 ... 9 forming parts of the tuned circuits of the oscillators 11, 12 ... 13 which are thereby caused to emit constant amplitude signals of frequencies F 1 +# 0 , F 2 +2# 0 , ... F n +n# 0 . The signals are mixed with the complex wave in mixers 14, 15 ... 16, the respective harmonics beating with these frequencies to produce frequencies F 1  ... F n  of amplitudes proportional to those of the harmonics. These may be converted to D.C. potentials by detectors 18, 20 ... 22 for feeding to the utilization apparatus 6 which is also fed with the fundamental frequency from the circuit 2. In a modification, Fig. 2 (not shown), the circuit 3 feeds only one thermionic reactance circuit to produce a frequency F+# 0  from which frequencies 2F+2# 0 , ... nF+n# 0  are produced by frequency multiplication for beating with the complex signal. In a further modification, Fig. 3 (not shown), even this thermionic reactance is eliminated by passing the fundamental through a limiter whose output is mixed with an oscillation F to produce the frequency F+f n .

:NGLETON 2,553,510

HRMONIC AMPLITUDE SELECTOR FOR SIGNALING SYSTEMS H. E. S

May 22, 951

'Filed Jan. 21, 195o 5 Sheets-Sheet 1 INVENTOR HF/W? Y E'. S//WLETOIV ATTORNEY May 22, 1951 H. E. slNGLEToN HARMONIC AMPLITUDE SELECTOR FOR SIGNALING SYSTEMS 3 Sheets-Sheet 2 A Filed Jan. 2l, 1950 INVENTOR HW? Y E. S/NGZ E70/V ATTORNEY May 22, 1951 H. E. SINGLETON 2,553,610

mmomc AMPLITUDE SELECTOR FOR SIGNALING SYSTEMS 5 sheets-smeet s Filed Jan. '21, 195o INVENTOR Hf/VPY E'. SNGLfTO/V ATTORNEY Patented May 22, 1 951 UNITED STATES PATENT OFFICE HARMQNIC AMPLITUDE SELECTOR FR SIGNALING SYSTEMS Henry E. Singleton, Cambridge, Mass., assigner to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware ApplicationJanuary 21, 1950, Serial No. 139,927 17 Claims. (Cl. 179`-1.5)

The present invention relates to a circuit arrangement for obtaining a measure of the amplitude of an electric wave subject to changes in frequency or of a plurality of such waves harmonically related to one another.

In pending application Ser. No. 50,516, filed July 24, '1948, by Jean B. Lair and Pierre R. Aigrain, there has been disclosed a communication system for the transmission of speech by Way of a channel of reduced band Width, as compared with the band width that would be necessary for transmitting the speech waves themselves, this being accomplished by deriving from the speech input a fundamental wave and a number of its harmonics (e. g. thirty), determining the relative amplitudes of these Waves, and transmitting indications of these amplitudes and, if desired, of the varying frequency of the fundamental to a receiving station where the original speech input may be substantially synthesized therefrom. A distinction is also made between voiced and unvoiced speech components, the fundamental wave being replaced in the case of the latter with an artificially generated oscillation of predetermined frequency.

jIn the above system the several harmonics are selected by means of tunable filters controlled from a pitch meter designed to select the fundamental and to produce an output which is a function of the frequency thereof. These filters, as more particularly disclosed in the pending application referred to, may be a series of mechanical-optical devices including, for example, screens of varying opacity driven at controllable speeds.

Broadly speaking, the invention has for its object to provide purely electrical means for determining the amplitude of a certain wave selected among a large number of oscillations, such as a mixture of voice frequencies present in speech, the selected Wave being subject to frequency changes in a determinable manner. More specifically, it is an object of this invention` to provide means of this description in or for a harmonics analyzer of the general type disclosed lin the above-identified application.

According to the invention, there is produced arreference wave of constantsamplitude the frequency of which consists of a fixed component (F) and a variable component (f) equal to the frequency of the selected wave, theA speech or other frequency mixture being then intermodulated with the reference Wave, whereupon on oscillation can be filtered out from the intermodulation products having a predetermined frequency (F) equal to that of the fixed component and having an amplitude proportional to` that of the selected wave in the frequency mixture.

To carry out the above method, the invention provides a source of oscillations controlled from a pitch meter to produce a wave of the form A cos [21r(F+f)t}-E] in which the amplitude A is constant, and ,f is a frequency equal or har- `monically related to that selected by the pitch and 1c is a proportionality factor and n is a phase angle.

More particularly, where the invention is applied to a harmonic analyzer as set forth above, the pitch meter may control a plurality of sources of oscillations having outputs in which the fixed component F may be the same or different for respective sources and in which the value of f ranges from a fundamental frequency fn through integral multiples 2in, 3ft thereof to ufo, n being, for example, of the order of thirty.

The invention Will be better understood from the following description of certain embodiments, reference being had to the accompanying drawings in which:

Figs. 1, 2 and 8 are respective block diagrams of different forms of amplitude selectors according to the invention; and

Fig. 4 is a block diagram of a pitch meter or fundamental frequency selector as used in the embodiments of the preceding figures.

lReferring to Fig. 1, there is shown an incoming line l to which a speech input or other mixture of frequencies is applied. A fundamental frequency selector 2, which together with an associated discriminator 3 constitutes what `in the foregoing and in the above-identified application has been referred to as a pitch meter, this pitch meter having a first output corresponding to the selected fundamental and a second output represented by a voltage proportional to the frequency thereof. The first output is applied over a line 4 to a utilization apparatus 6 (which may be a transmitter, recorder or any suitable responsive device), the second output being applied over a line 5 to the grids of a plurality .of reactance tubes 1, 8 and 9 in parallel. The

u www speech input is also applied to a line I in parallel with the pitch meter 2, 3.

Each of the reactance tubes I, 8 and 9 forms part of the tank circuits of respective oscillators II, I2 and I3. The output voltage of discriminator 3, varying with the selected fundamental frequency fo, controls the reactances of these tubes in such manner that the operating frequencies of the oscillators shown have the values Fi-I-fo, F24-Efo, and Fn-i-nfn, it being understood that a number of intervening oscillators operating at frequencies Fs-I-Bfo F(n 1)+(1z-llfo, respectively, have not been illustrated.

Oscillators II, I2 and I3 work into respective mixers I4, I5 and it each of which also derives an input from the line Iii. These mixers may be of any non-linear type to provide intermodulation. The output of mixer Iii contains a component of frequency F1 the amplitude of which varies proportional to that of the oscillation of frequency jo in the speech input; this component is separated out by a lter II and its amplitude detected in a detector IB. Similarly, the output of mixer I5 contains a component of frequency F2 and of an amplitude proportional to that of the second harmonic of the aforesaid oscillation fo, this component being selected and detected by means of a lter I9 and a detector 20. In a like manner the mixer I6 works into a filter 2|, tuned to a frequency Fn, which in turn feeds a detector 22. The outputs of all detectors, such as I8, 26 and 22, are applied to the utilization apparatus 8.

A delay network 23 may be inserted in the line I0, ahead of the rst mixer I4, for the purpose of compensating for any delay introduced in the pitch meter 2, 3. Since, however, the amplitudes of the oscillation fo and its harmonics vary at a relatively slow rate only (not more than about 25 cycles per second), minor uncompensated delays may not be objectionable.

In the modification of Fig. 2, elements corresponding to those of Fig. 1 have been given the same reference numerals. Instead of providing a separate oscillator for each mixer, the oscillator I I works into a plurality of frequency multipliers such as a doubler 24, a tripler 25 and a multiplier 26. The frequency doubler 2li is the functional equivalent of oscillator I2 (Fig. l) and produces an output of frequency FH-Zu wherein Fz--2F (F being the fixed component of the output of oscillator I I). Similarly, the multiplier 26 is the functional equivalent of oscillator I5 and produces an output of frequency nF-I-nfu. Frequency tripler 25 serves for the selection of the third harmonic of the fundamental fo and works into a mixer 21, the latter feeding a detector 29 by Way of a filter 28 tuned to the frequency 3F.

In the embodiment of Fig. 3, wherein elements having equivalents in Figs. 1 and 2 have again been designated by the same reference characters, the pitch meter comprising the fundamental frequency selector 2 is shown to include a limiter 3G in lieu of the discriminator 3. This limiter works into a mixer 3l which, being fed from an oscillator S2 having a xed operating frequency F, takes the place of the oscillator II in that it produces a reference wave of frequency F-I-fo. The mixer 3| feeds the frequency doubler 24, the frequency tripler 25 and a plurality of additional frequency multipliers (not shown) by way of connections indicated at 33 and 34. The frequency doubler Z5 Works into a second doubler 35.serving to select the fourth harmonic of the fundamental derived from the pitch meter 2, 30. A mixer 36, a lter 31 and a detector 33 cooperate, accordingly, with the frequency doubler 35, the lter 3'1 being tuned to the frequency 4F.

Frequency tripler 2'5 and frequency doublers 25 and 35 may feed further multipliers (not shown) in cascade therewith for the purpose of producing harmonics of such orders as are not prime members, e. g. the sixth, eighth, ninth, etc. harmonics of the output of mixer 3|. This is indicated by the provision of additional output connections 39, 4U and 4I.

It will be observed that in the embodiments of Figs. 2 and 3 the fixed components of the various reference Waves are necessarily multiples of the basic carrier wave F, whereas in the form of the invention shown in Fig. 1 they may assume any value, for example be identical (thus :F10 The frequencies F may, for example, be of the order of one or several kilocycles per second. f

Fig. 4 shows in greater detail the portion 2 of the pitch meter used in the circuit arrange.- ments of Figs. 1, 2 and 3. It comprises a band pass filter 42 the pass band of which extends over a range which includes the second and third harmonics of the desired fundamental frequency fu, or any other adjacent two harmonics thereof, bearing in mind the fact that fo is variable within certain limits. (The reason for selecting a` pass band encompassing the harmonics rather than the fundamental itself is that the latter is often suppressed in actual speech reproduction.) The output of filter 42 is applied to a non-linear device, e. g. a rectifier or detector, where the two harmonics are intermodulated to produce the de-- sired fundamental. A sloping filter 44, followed by a sloping amplifier 45, then serves to select the fundamental among the other intermodula;

In conformity with the teachings-of the abovei identified application, the pitch meter may also be provided with means for generating a syn.

thetic fundamental wave of predetermined frequency (say, 50 cycles per second) if the frequency of the fundamental actually detected falls below a certain level, thus indicating an unvoiced input. Such an arrangement, however, has not been illustrated inasmuch as it forms no further part of the present invention.

While the invention has been described with reference to certain particular embodiments, it

is to be understood that the same have been` given merely by Way of illustration and not as a limitation upon the spirit and scope of the invention as dened in the objects and in the appended claims.

What is claimed is:

1. A circuit arrangement for obtaining a mease ure of the amplitude of a selected electric wave subject to changes in frequency, said wave forming part of a mixture of several oscillations, comv` prising a pitch meter adapted to derive from said mixture an output representative cf the frequency of said selected wave, a variable source of oscillations, circuit means for applying said output to said source in such manner as to operate said source to produce a reference oscillation having a fixed component and a variable component harmonically related to the frequency of said selected wave, mixer means for superheterodyning said mixture with said reference oscillation, and filter means for selecting from the output of said mixer means a resultant oscillation cf a frequency equal to said fixed component, said resultant oscillation having an amplitude proportional to that of said selected wave.

2. A circuit arrangement according to claim 1 wherein said source comprises an oscillator having a tank circuit and said circuit means comprises a reactance tube forming part of said tank circuit.

3. A circuit arrangement according to claim 1 wherein the output of said pitch meter is a wave of constant amplitude and cf a. frequency equal to that of said selected wave, said source comprising an oscillator having an operating frequency equal to said fixed component and mixer means for modulating said operating frequenceT with said output of the pitch meter.

4. A circuit arrangement for measuring the relative amplitudes of a plurality of harmonically related oscillations forming part of a frequencj mixture, said oscillations being subject to changes in Ifrequency, comprising a pitch meter adapted to select the fundamental frequency of said harmonically related oscillations from said mixture and to produce an output representative of said fundamental frequency, a plurality of variable sources of oscillations, circuit means for applying said output to said sources in such manner as to operate said sources to produce respective reference waves of the form A cos [21r(F-if)t+l wherein A is an amplitude fixed for each source, F is a frequency component fixed for each source and f is a frequency corresponding to a different harmonic of said fundamental frequency for each of said sources, a plurality of mixer means for superheterodyning said respective reference waves with said frequency mixture, and a plurality of lter means for selecting from the output of each of said mixer means a resultant oscillation of the form cAa. cos [2Ft-l-17] wherein k is a proportionality factor and a is the amplitude of a respective one of said harmonically related oscillations.

5. A circuit arrangement according to claim 4, comprising a plurality of detector means respectively connectedto said mixer means for producing an output proportional to said amplitude a.

6. A circuit arrangement according to claim 5, comprising utilization means connected to all of said detector means to receive the said output thereof and further circuit means for applying a wave of said fundamental frequency from said pitch meter to said utilization means.

7. A circuit arrangement according to claim l wherein each of said sources comprises a separate oscillator.

8. A circuit arrangement according to claim 7 wherein each of said oscillators is provided with a tank circuit including a reactance tube, said circuit means including discriminator means adapted to derive from the fundamental frequency selected by said pitch meter a voltage proportional to said fundamental frequency and to apply said voltage to all of said reactance tubes.

9. A circuit arrangement according to claim s wherein said sources include oscillator means controlled from said pitch meter and frequency mul tiplier means controlled from said oscillator means.

l0. A circuit arrangement according to claim 9 wherein said oscillator means is provided with a tank circuit including a reactance tube, said circuit means including discriminator means adapted to derive from the fundamental frequency selected by said pitch meter a voltage proportional to said fundamental frequency and to apply said voltage to said reactance tube.

l1. A circuit arrangement according to claim 4 wherein said sources include an oscillator of fixed operating frequency and mixer means connected to said pitch Imeter for modulating said operating frequency with the fundamental frequency selected by the pitch meter.

l2. A circuit arrangement according to claim 11 wherein said sources further include a plurality of frequency multipliers connected to be controlled from said mixer means for producing harmonics of the output of said mixer.

13. A circuit arrangement according to claim 12 wherein at least some of said multipliers are connected in cascade.

14. A circuit arrangement according to claim 4 wherein said sources include a rst source controlled from said pitch meter and a plurality of frequency multipliers connected to be controlled from said first source for producing harmonics of the output of said rst source.

l5. A circuit arrangement according to claim 14 wherein at least some of said multipliers are connected in cascade.

16. A circuit arrangement according to claim Li wherein said fixed component F is the same for all of said sources.

17. A circuit arrangement according to claim 4 wherein the fixed components F of all of said sources, respectively, are harmonically interrelated.

HENRY E. SINGLETON.

No references cited. 

